Mirrorback coating

ABSTRACT

A composition capable of being applied as a film and hardening to form a protective layer on the back of a mirror comprises a fluid organic resin and a corrosion inhibitor selected from the group consisting of dicyandiamide and metal or acid salt thereof. The organic resin may be any thermoplastic or thermosetting resin suitable for coating the reflective and other metallic layers of the mirror. Exemplary resins include alkyd resins, acrylic resins, modified alkyd resins, polyesters, urethane oils, vinyl halide polymers or copolymers, oleoresinous varnishes, nitrocellulose compositions, phenol-formaldehyde resin varnishes, and epoxy resins. Preferably, the resin is an alkyd or modified alkyd resin. The dicyandiamide or metal or acid salt of dicyandiamide may be present in an amount from about 0.1 to 20 weight percent, preferably 0.5 to 10 weight percent, of the organic resin coating system. The resin system should be essentially free of lead and lead salts. To inhibit the corrosion of metallic film layers on mirrors, a mirror having a glass substrate layer and a metallic film layer thereover should be obtained, after which the fluid organic resin coating system containing the dicyandiamide or metal or acid salt of dicyandiamide corrosion inhibitor is applied over the metallic film layer. The organic resin coating system is then hardened to produce the protective coating layer over the metallic layer. Other articles having metallic surfaces may also be protected by the dicyandiamide-containing resin system of the present invention.

BACKGROUND OF THE INVENTION

This invention relates to a coating for use on mirror backs, and, inparticular, to a lead-free organic coating to be applied to the metallicfilm layer on the back of a mirror to protect the metallic layer andprevent corrosion thereof.

Typical mirrors are made of a glass sheet and a thin layer of a metallicfilm applied to the back of the sheet. The metallic film layer adhereddirectly to the glass is usually a film of silver, although othermetallic films may also be used, such as copper. When silver is used asthe primary reflective layer, it is commonly protected by a secondmetallic film layer of copper or some other metal.

It has long been known to employ various paints and other film-formingorganic resins as a further protective layer over a metallic film layerto protect the layer from corrosion and physical damage. Traditionally,these paints have included lead-based corrosion inhibitors, such as leadsalts. However, in recent times, both users and producers of such paintproducts have sought to eliminate the use of lead and lead compounds forhealth and environmental reasons. A recent effort in this direction isreflected in U.S. Pat. No. 4,707,405 to Evans et al directed to use ofcyanamide salts of non-lead metals as corrosion inhibitive pigments inmirror back coatings. This patent discloses the use of such non-leadcyanamide salts as calcium cyanamide and zinc cyanamide in various typesof film-forming thermosetting or thermoplastic resins which are appliedover the silver and copper layers on the backs of mirrors. Continuingefforts have been made to produce an effective lead-free corrosioninhibiting mirror back coating to satisfy the long felt need of theindustry, but to date, no such commercial coatings have proven to be aseffective in inhibiting corrosion and overall protection as leadcontaining coatings.

Bearing in mind the problems and deficiencies of the prior art, and thelong felt need of industry, it is therefore an object of the presentinvention to provide an effective corrosion inhibiting, lead-freecoating for covering the metallic film layers on the back of a mirror.

It is another object of the present invention to provide an organicfilm-forming resin which incorporates a non-lead corrosion inhibitorwhich can be easily applied by existing techniques to mirror backs. .Itis a further object of the present invention to provide a lead-freepaint for protecting thin silver and/or copper or other metallic filmlayers which imparts corrosion protection of equal to or greatereffectiveness than prior art lead containing paints.

It is yet another object of the present invention to provide aneffective process for inhibiting corrosion of metallic film layers onmirrors.

It is a further object of the present invention to provide mirror andother articles having effective protection of their metallic film layersagainst salt spray and other corrosion-causing compounds.

SUMMARY OF THE INVENTION

The above and other objects, which will be apparent to those skilled inthe art, are achieved in the present invention which provides acomposition comprising a paint or other fluid organic resin coatingsystem capable of being applied as a film and hardened to form aprotective layer, the resin additionally containing a corrosioninhibitor selected from the group consisting of dicyandiamide and metalor acid salts thereof. The term "hardened" is used to mean that thecoating system can be cured if the resins are thermosetting or dried ifthe resins are thermoplastic. The organic resin employed in the coatingsystem can be any thermoplastic or thermosetting resin suitable forcoating a metallic layer such as that found on the back of a mirror.Exemplary resins include alkyd resins, acrylic resins, acrylic and othermodified alkyd resins, polyesters, urethane oils, vinyl halide polymersor copolymers, oleoresinous varnishes, nitrocellulose compositions,phenolformaldehyde resin varnishes, and epoxy resins. Preferably, theresin is an alkyd or modified alkyd resin, more preferably anacrylic-alkyd copolymer phenolic resin system.

The dicyandiamide or metal or acid salt of dicyandiamide may be presentin an amount from about 0.1 to 20 weight percent, preferably about 0.5to 10 weight percent, of the organic resin coating system (includingresins, solvents and other additives). Preferably, the organic resinshould be essentially free of lead and lead salts, either as corrosioninhibitors or other components.

To inhibit the corrosion of metallic film layers on mirrors, a mirrorhaving a glass substrate layer and a metallic film layer thereovershould be obtained, after which the fluid organic resin coating systemcontaining the dicyandiamide or metal or acid salt of dicyandiamidecorrosion inhibitor is applied over the metallic film layer. The organicresin coating system is then hardened to produce a protective coatinglayer over the metallic layer.

The preferred mirror article contains, in sequence, the glass substrate,the metallic film layer(s) which may be silver and/or copper or someother metal, and the hardened organic resin system as described above.Preferably, the mirror has a thin layer of silver film attached directlyto the glass layer as the reflective layer, a thin protective layer of acopper film over the silver layer, and the hardened coating systemdescribed above directly over the copper film layer as the primarycorrosion inhibitor layer. Other articles having metallic surfaces maybe protected by the dicyandiamide-containing resin systems describedabove as well.

DETAILED DESCRIPTION OF THE INVENTION

The mirrors and metallic film layers on which the coating of the presentinvention has been found to be particularly useful are those in whichone or more layers of silver and/or copper films have been applied to aglass substrate, although the coating may also be useful over filmlayers of other metals as well. Preferably, the mirror consists of asubstrate layer of glass and a layer of reflective silver or copper filmapplied to the rear surface of the glass. If a silver film is applieddirectly to the glass, it is common to apply a second film layer ofcopper over the silver to provide protection against corrosion andphysical damage to the silver layer. Such metallic film layers arerelatively thin and on the order of approximately 700 angstroms for thesilver layer and approximately 220 angstroms for the copper layer.

Such mirrors may be made by any of the known processes in the prior art.The glass surface to which the metallic film layer is to be applied isusually lightly polished and cleaned and thereafter sensitized with anaqueous stannous chloride solution. The silver film layer may bedeposited on the sensitized glass surface by one of many methods such asthat described in U.S. Pat. No. 4,737,188 to Bahls, the disclosure ofwhich is hereby incorporated by reference, in which an N-methylglucaminereducer is utilized with ammoniacal silver nitrate and a strong basesuch as sodium hydroxide in aqueous solutions sprayed on and combined atthe sensitized glass surface to deposit the silver film. Thereafter, acopper film may be applied to and over the silver film by any one of avariety of prior art procedures such as a galvanic process whichutilizes aqueous suspensions of iron and copper powder or by thedisproportionation of cuprous ions on the silver surface. The latterprocess is described in U.S. Pat. No. 3,963,842 to Sivertz et al, thedisclosure of which is hereby incorporated by reference. In suchprocess, a cupric tetraammonium sulfate solution is reduced bycombination with hydroxylamine sulfate and thereafter reacted with anactivator-modifier such as a mixture of citric acid or ethylene diamineand H₂ SO₄ to form a copper film on the silvered surface.

The coating of the present invention to be applied over the copper,silver or other metallic film layer is based on any suitablethermosetting or thermoplastic organic film-forming resin. Thethermosetting resins contemplated in use in the present invention arethose that require heat to effect curing, such as by infrared heating,although room temperature air drying resins are also included.

Suitable resins include alkyd resins, acrylic resins, polyesters,urethane oils, vinyl halide polymers or copolymers, oleoresinousvarnishes, nitrocellulose compositions, phenol-formaldehyde resinvarnishes, epoxy resins, or combinations of such resins. Preferably, theresins employed in the present invention are alkyd or modified alkydresins such as acrylic-alkyd copolymers in combination with a solvent,and other additives such as a pigment, if desired, to produce a resincoating system. Such alkyd resin systems may be modified with acrylics,urethanes and polyurethanes, phenolics, and combinations of the above.More preferably, the resins may be acrylic-alkyd copolymers and phenolicresins in combination. Amino crosslinking agents such asmelamine-formaldehyde resins and/or urea-formaldehyde resins may beincluded in the modified alkyd or other resin system to make the systemheat-curable. Alternatively, metal driers can be employed in the systemto make it air drying.

The resin system of the present invention should employ a binder resinwhich casts a suitable film and provides good adhesion to and over theaforementioned metallic film layer(s). The system may employ a suitablesolvent of the type normally employed in the particular resin system.For example, in the preferred alkyd and modified alkyd resin systems ofthe present invention, an ester such as propylene glycol monomethylether acetate, butyl acetate or isobutyl acetate may be employed.Preferably, the alkyd or modified alkyd resins comprise 20 to 50 percentby weight of the system, more preferably 20 to 35 weight percent. Thesolvents or solvent blends employed in this system are preferably 20 to35 percent by weight of the system. Additives normally employed in resincoating systems for this type of application may also be added inaddition to the resin and solvent, for example, pigments (where it isdesired to impart a color) and inert fillers or extenders such asbarytes or calcium carbonate; flow additives; anti-settling agents tosupport any dense pigment particles; catalysts such as blocked orunblocked acids (where a thermosetting resin is employed); surfaceactive agents; antiskinning agents such as methyl ethyl ketoxime; andadditives for other purposes.

The aforementioned resin systems are by themselves fully hardenable toform a film over a metallic film layer. To impart effective corrosionresistance for the metallic film layer, the present inventionspecifically contemplates the use of a compound selected from the groupconsisting of dicyandiamide (also known as "cyanoguanidine"), metal oracid salts thereof, or combinations of the above. Unless specifiedotherwise, references herein to use of dicyandiamide shall also apply tometal or acid salts of dicyandiamide, in connection with the corrosioninhibitor of the present invention. The dicyandiamide may be employed ina range from about 0.01 to about 20% by weight of the resin coatingsystem, although the range from about 0.1 to about 10% is preferred.More preferably, a range from about 0.5-1% to about 5% is employed formaximum effectiveness. At the higher amounts, particularly above 10%,the dicyandiamide becomes particularly susceptible to reaction withwater, for example, any moisture present in the environment. If suchhigher amounts of the dicyandiamide are employed in the resin coatingsystem of the present invention, it is preferred that an additionalwater or moisture proof coating be applied over the hardened resincoating. The dicyandiamide may be blended with the resin system bycomminuting it into fine particles, preferably from 10 to 20 microns orless in size. It has been found that when the small size particles areemployed, a lower overall weight percentage of dicyandiamide is neededto achieve a desired level of corrosion protection, since the smallerparticle size can be dispersed throughout the resin to a greater extentto provide the necessary protection. Alternatively, the dicyandiamidemay be dissolved in a suitable solvent and dispersed and blended intothe resin system.

While not wishing to be limited by theory, it is thought that thedicyandiamide reacts in the present system to: (1) passivate themetallic film on which it is applied, for example, a copper film, andcreate a complex with the metal to reduce corrosion; (2) increase theadhesion of the metal film, such as copper, to the cured resin; or (3) acombination of 1 and 2 above.

The dicyandiamide corrosion inhibitor is incorporated instead ofutilizing conventional lead based pigments, such as lead salts, employedin the past. However, other corrosion inhibitors may be used inconjunction with the dicyandiamide, such as zinc oxide, to provide adesired degree of protection in a specific application. If desired, lowamounts of leaded materials which comply with environmental laws andregulations may be added to the resin system. Preferably, the blendedresin system to be applied over the aforementioned metallic films iscompletely free of lead to comply more easily with environmental lawsand regulations in its manufacturing and use.

The blended resin system employing the dicyandiamide and/or its metal oracid salts is applied to the metallic layers on the mirror backs byconventional processes, such as air or airless spraying (preferably thelatter), roller coating, or curtain coating. Thermosetting resin systemssuch as the aforementioned preferred alkyd or modified alkyd resinsystems may be dried by infrared heating, typical conditions being fiveminutes heating time with an exit film temperature of about 250° F.(120° C.). The thickness of the dried resin film layer may be up to0.002 in. (51 microns) thick, although it is preferred that the filmthickness be from about 0.001 to 0.0015 in. (25 to 38 microns) inthickness. Where thicker coatings are desired, multiple layers of thecoating may be applied. The use of the thin layers described aboveenables the applied resin system to be quickly dried to a hardened layerwithout causing bubbles or other defects. The resin system incorporatingthe dicyandiamide of the present invention provides good protection tothe edges of the mirror metallic film layers, at which locationcorrosion usually commences. Mirror edge corrosion (also known as "blackedge") can occur because of moisture present in bathrooms or other highhumidity environments. Other causes include the use of certain adhesivesin which a component (for example, acetic acid in silicone basedadhesives) can attack the resin coating layer and metallic film. Also,where the edges of the mirrors are bevelled or polished with anabrasive, abrasive coolant having a high pH level can remain on the edgeand attack the paint and metallic film layers of the mirror.

In addition to providing good corrosion protection, the resin coatingsystem employing the dicyandiamide of the present invention should beable to provide a smooth finish having a good appearance, and, if themirror is later cut or otherwise handled, should prevent chipping of theresin paint at the mirror edges.

The following non-limiting examples are provide to illustrate resinsystems employing dicyandiamide of the present invention.

EXAMPLES

A series of glass panels were cleaned, sensitized, and coated withsuccessive layers of a silver film and a copper film according to theprocesses described above. The resulting silver film layer wasapproximately 700 angstroms thick and the resulting copper film toplayer was approximately 220 angstroms thick.

Mirror back paint coatings to be applied over the silver and copperlayers were prepared by mixing starting compositions A and B as follows(components reported in parts by weight):

    ______________________________________                                                              Composition:                                            Component               A       B                                             ______________________________________                                        acrylic-alkyd copolymer 20.4    36                                            (Freeman Chemical Chempol 13-1214)                                            phenolic resin solution 10.9    --                                            (44.5% Union Carbide Corp. Ucar                                               CK2400; 22.2% mineral spirits;                                                22.2% butyl alcohol; 11.1% xylene)                                            carbon black             0.8    --                                            (Pfizer Superjet LB-1011)                                                     barium sulfate          27.3    --                                            (Thompson Weiman Barimite XF)                                                 6% cobalt naphthenate    0.18   --                                            (Celanese Corp.)                                                              6% manganese naphthenate                                                                               0.14   --                                            (Mooney Chemical)                                                             methyl ethyl ketoxime    0.8    --                                            (Tenneco Chemical Exkin 2)                                                    propylene glycol monomethyl ether                                                                     13.6    28                                            acetate                                                                       (Dow Chemical PM acetate)                                                     xylene                   8.5    --                                            talc                    17.0    --                                            (Cyprus Minerals Mistron                                                      Monomix)                                                                      dicyandiamide           --      36                                            ______________________________________                                    

The components of each of the compositions A and B were dispersed bygrinding to a particle size of 6 on the Hegman Scale.

Compositions A and B were combined in amounts of 100 g and 120 g,respectively, along with 20 g of the acrylic acid copolymer and 10 g ofthe phenolic resin solution to produce resin coating system sample no. 1containing 17.3% dicyandiamide. Six additional different resin systemswere prepared by combining different amounts of compositions A and B toproduce resin system samples 2 through 7 containing dicyandiamide in thefollowing respective amounts: 8.6%, 4.3%, 2.9%, 0.8%, 0.12% and 0.015%.Additional amounts of the aforementioned resins and pigments were addedas necessary to maintain an approximately equal ratio of pigment toresin throughout the different resin systems. A control sample resinsystem was prepared in the same pigment to resin ratio, but without anydicyandiamide. Table I shows the compositions of the aforementionedsamples.

The eight different liquid resin coating systems (seven withdicyandiamide corrosion inhibitor, one control) were applied to thecopper layer on the backs of the aforementioned mirrored glass samplesusing a draw down bar and thereafter infrared drying at about 250° F.(120° C.) for approximately five (5) minutes until cured to a hardenedfilm layer of approximately 0.001 in. (25 microns) thickness.

The coated mirror samples were then subjected to a corrosion test in a20% salt spray environment for 150 hours pursuant to Federalspecification DD-M-00411 b. Following completion of the test the mirrorswere evaluated for corrosion by noting the appearance of the silver (andother film layers) from the front of the mirror.

                                      TABLE 1                                     __________________________________________________________________________                   Samples: (in parts by weight)                                                 1  2   3   4   5   6   7   Control                             __________________________________________________________________________    Composition A  100.0                                                                            100.0                                                                             100.0                                                                             100.0                                                                             100.0                                                                             100.0                                                                             100.0                                                                             100.0                               Composition B  120.0                                                                            60.0                                                                              30.0                                                                              20.0                                                                               5.0                                                                               0.8                                                                               0.11                                                                             --                                  acrylic-alkyd copolymer                                                                       20.0                                                                            41.6                                                                              52.4                                                                              56.0                                                                              61.4                                                                              62.9                                                                              63.16                                                                             63.2                                phenolic resin solution                                                                       10.0                                                                            10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                                                              10.0                                propylene glycol monomethyl                                                                  -- 16.8                                                                              25.2                                                                              28.0                                                                              32.2                                                                               33.37                                                                            33.58                                                                             33.6                                ether acetate                                                                 Talc           -- 21.6                                                                              32.4                                                                              36.0                                                                              41.4                                                                              42.9                                                                              43.16                                                                             43.2                                __________________________________________________________________________

                                      TABLE II                                    __________________________________________________________________________                             density                                                                              spot                                          Sample                                                                             wt. % Dicyandiamide                                                                      black edge (mm)                                                                        of spots                                                                             size                                          __________________________________________________________________________    1    17.3       Total Failure                                                                          (clear glass)                                        2    8.6          1 mm   dense  1-2 mm                                        3    4.3        0.3 mm   medium pin points                                    4    2.9        0.3 mm   very few                                                                             pin points                                    5    0.8        0.3 mm   medium faint pin points                              6     0.12      0.3 mm   medium large spots                                   7     0.015     Total Failure (film still attached)                           Control                                                                            0.0        Total Failure (clear glass)                                   __________________________________________________________________________

Both the control sample and the sample having the 17.3% dicyandiamideresin showed complete failure of the metal film layers as they and theresin film layer had peeled off the glass layer. The samples having the2.9% and 0.8% dicyandiamide resin had very good appearance with onlyfine pinpoints visible on the silver film layer and minimal corrosion atthe mirror edges. The samples having the 8.6%, 4.3%, 0.12% and 0.015%dicyandiamide resin showed corrosion between the two extremes describedabove. The results of the salt spray test are shown in Table II. Exceptfor the sample having the 17.3% dicyandiamide resin, the presence ofdicyandiamide in the resin system resulted in marked improvement incorrosion testing, as compared to the control sample having nodicyandiamide. This is best shown by the reduced edge creep on themirror samples. It is believed that the failure of the sample having the17.3% dicyandiamide resin resulted from reaction of the dicyandiamidewith water, which reaction may be prevented by use of a water ormoisture proof top coat over the resin system of the present invention.

The aforementioned examples of resin systems including the dicyandiamidecorrosion inhibitor of the present invention may be further modified,for example, by including other pigments such as zinc oxide or titaniumdioxide in part replacement for the talc, or by using additional resinin part replacement for the pigments to achieve better corrosionresistance. In addition to protection of film layers of mirrors, asdescribed above, the dicyandiamide containing resins of the presentinvention may be applied to and over metallic surface layers, such ascopper, copper-based alloys, silver, or silver based alloys of otherarticles to provide enhanced corrosion protection.

While the invention has been described with reference to specificembodiments, it will be recognized by those skilled in the art thatvariations are possible without departing from the spirit and scope ofthe invention, and that it is in ten ded to cover all changes andmodifications of the invention disclosed herein for the purposes ofillustration which do not constitute departure from the spirit and scopeof the invention.

Having thus described the invention, what is claimed is:
 1. A processfor inhibiting corrosion of metallic film layers on mirrors comprisingthe steps of:(a) obtaining a mirror having a glass substrate layer andmetallic film layer attached to the glass layer; (b) applying to saidmetallic film layer a blended fluid organic resin coating systemcontaining a corrosion inhibitor selected from the group consisting ofdicyandiamide and metal or acid salts thereof; and (c) hardening theresin system to produce a protective coating layer over said metalliclayer.
 2. The process of claim 1 wherein said resin system includes anorganic resin selected from the group consisting of alkyd resins,acrylic resins, modified alkyd resins, polyesters, urethane oils, vinylhalide polymers or copolymers, oleoresinous varnishes, nitrocellulosecompositions, phenol-formaldehyde resin varnishes, melamine formaldehyderesins, urea formaldehyde resins, epoxy resins, and combinations of theabove.
 3. The process of claim 1 wherein said corrosion inhibitor ispresent in an amount of about 0.1 to 20 weight percent of said organicresin coating system.
 4. The process of claim 1 wherein said metallicfilm layer comprises one or more layers of a metal selected from thegroup consisting of silver and copper.
 5. The process of claim 1 whereinsaid hardened coating layer is attached to a copper film layer.
 6. Theprocess of claim 1 wherein said hardened coating layer is attached to asilver film layer.
 7. The process of claim 1 wherein said hardenedcoating layer is lead-free.
 8. The process of claim 1 wherein saidcorrosion inhibitor is present in an amount of about 0.5 to 5 weightpercent of said organic resin coating system.
 9. A process forinhibiting corrosion of a metallic surface comprising the steps of:(a)obtaining an article having a metallic surface; (b) applying to saidmetallic surface a blended liquid organic resin system, selected fromthe group consisting of alkyd resins, modified alkyd resins, acrylicresins, melamine formaldehyde resins, urea formaldehyde resins, andcombinations of the above, and containing a corrosion inhibitor selectedfrom the group consisting of dicyandiamide and metal or acid saltsthereof; and (c) hardening the resin system to produce a protectivecoating layer over said metallic surface.
 10. The process of claim 9wherein said metallic surface is made of copper or a copper based alloy.11. The process of claim 9 wherein said metallic surface is made ofsilver or a silver based alloy.
 12. The process of claim 9 wherein saidcorrosion inhibitor is present in an amount of about 0.1 to 10 weightpercent of said organic resin coating system.
 13. a process forinhibiting corrosion on mirrors comprising the steps of:(a) obtaining aglass substrate; (b) applying one or more metallic film layers to saidglass substrate to produce a mirror, said metallic film being selectedfrom the group consisting of copper and silver films; (c) applying alead-free, blended fluid organic resin coating system to said metallicfilm, said resin coating system containing a corrosion inhibitorselected from the group consisting of dicyandiamide and metal or acidsalts thereof in an amount of about 0.1 to 10 weight percent of saidresin coating system; and (d) hardening the resin system to produce aprotective coating layer over said metallic film layer.
 14. The processof claim 13 wherein said resin system includes an organic resin selectedfrom the group consisting of alkyd resins, acrylic resins, modifiedalkyd resins, polyester, urethane oils, vinyl halide polymers orcopolymers, oleoresinous varnishes, nitrocellulose compositions,phenol-formaldehyde resin varnishes, melamine formaldehyde resins, ureaformaldehyde resins, epoxy resins, and combinations of the above. 15.The process of claim 13 wherein said corrosion inhibitor is present inan amount of about 0.5 to 5 weight percent of said organic resin coatingsystem.
 16. The process of claim 13 herein said resin system is cured toform said protective coating layer.
 17. The process of claim 13 whereinsaid resin system is dried to form said protective coating layer. 18.The process of claim 1 wherein said corrosion inhibitor isdicyandiamide.
 19. The process of claim 1 wherein said corrosioninhibitor is a metal or acid salt of dicyandiamide.
 20. The process ofclaim 1 wherein said organic resin coating system is selected from thegroup consisting of alkyd resins, modified alkyd resins, acrylic resins,melamine formaldehyde resins, urea formaldehyde resins, and combinationsthereof.
 21. The process of claim 2 wherein said corrosion inhibitor isdicyandiamide.
 22. The process of claim 2 wherein said corrosioninhibitor is a metal or acid salt of dicyandiamide.
 23. The process ofclaim 9 wherein said corrosion inhibitor is dicyandiamide.
 24. Theprocess of claim 9 wherein said corrosion inhibitor is a metal or acidsalt of dicyandiamide.
 25. The process of claim 13 wherein saidcorrosion inhibitor is dicyandiamide.
 26. The process of claim 13whereins aid corrosion inhibitor is a metal or acid salt ofdicyandiamide.
 27. The process of claim 13 wherein said organic resincoating system is selected from the group consisting of alkyd resins,modified alkyd resins, acrylic resins, melamine formaldehyde resins,urea formaldehyde resins, and combinations thereof.
 28. The process ofclaim 14 wherein said corrosion inhibitor is dicyandiamide.
 29. Theprocess of claim 14 wherein said corrosion inhibitor is a metal or acidsalts of dicyandiamide.
 30. A process for inhibiting corrosion onmirrors comprising the steps of:(a) obtaining a mirror having a glasssubstrate layer and metallic film layer attached to the glass layer,said metallic film being selected from the group consisting of copperand sivler films; (b) applying an essentially lead-free blended liquidorganic resin containing a corrosion inhibitor in an amount of about 0.1to 10 weight percent to said metallic film layer, said resin coatingsystem being selected from the group consisting of alkyd resins,modified alkyd resins, acrylic resins, melamine formaldehyde resins,urea formaldehyde resins, and combinations of the above, said corrosioninhibitor being selected from the group consisting of dicyandiamide andmetal or acid salts thereof; and (c) hardening the resin system toproduce a protective coating layer over said metallic film layer. 31.The process of claim 30 wherein said corrosion inhibitor isdicyandiamide.
 32. The process of claim 30 whereins aid corrosioninhibitor is a metal or acid salt of dicyandiamide.